Resolve short names on the caller's domain with FMSG_DEFAULT_DOMAIN=caller

[markmnl]

Summary

A server that serves callers on several domains can't use one server-wide FMSG_DEFAULT_DOMAIN. This adds a reserved value, FMSG_DEFAULT_DOMAIN=caller (case-insensitive). With it, short names resolve on the domain of the address the server acts as for each request. For example, bob becomes @bob@example.org for @mark@example.org and @bob@example.net for a caller on example.net.

• HTTP (API key, OAuth, combined): uses the per-request caller address.
• stdio: uses the configured key's address. send_message, reply, add_recipients and wait_for_message (from) already resolve the caller first. In caller mode, resolve_address now does the same, which can trigger the token exchange. It resolves locally in every other mode, as before.
• whoami: default_domain and the line "Short names resolve to @name@." show the caller's domain.
• Server instructions: name the caller's domain when the address is known: always for HTTP sessions, and for stdio once the startup address lookup succeeds. Otherwise they say short names resolve on the caller's own domain.
• Precedence: directory entries still come first. A fixed or unset FMSG_DEFAULT_DOMAIN behaves as before, and the resolution value stays default_domain.

Implementation: CALLER_DOMAIN and effectiveDefaultDomain() in src/address.ts. AddressResolver gains an optional callerAddress, and resolverFor(deps, caller) in src/tools/common.ts builds the per-caller resolver.

Docs: README env table, --help, docs/http-deployment.md and CHANGELOG (Unreleased).

Tests

New test/default-domain.test.ts covers:

• config parsing of caller, CALLER and @Caller, plus real and empty values
• resolveAddress with a caller domain, directory precedence, a missing caller address, and a fixed or unset domain
• instruction text for each case
• stdio resolution after the token exchange
• HTTP with two API-key callers and with two OAuth callers on different domains: each one's whoami, resolve_address, send_message and instructions use its own domain
• a fixed domain and an unset domain over HTTP, both unchanged

npm run typecheck and npm test pass (165 tests).

🤖 Generated with Claude Code